"These were Tribune's softest numbers in at least two years," the analyst added, saying the December results "reflect a further deterioration in ad revenue momentum."

The U.S. newspaper industry has long been facing a gradual and apparently irreversible decline in readership. But the circulation decline has accelerated in recent years, in part because more Americans are opting to get their news from the Internet.

In addition, a growing number of people are using Web sites to find jobs, locate apartments and sell their cars--a trend that is squeezing classified-ad revenues at papers.

Television broadcasters are facing some of the same revenue pressures. Tribune television revenues fell 10 percent in the month. Technological advances such as TiVo allow viewers to skip past advertising. And high-speed Internet connections make it easier for people to forsake TV in favor of Web-based activities.

What's more, advertisers who once placed only print and broadcast advertising now have a third, fast-growing platform with attractive demographics: Internet ads.

The effects of those industry dynamics were evident in the latest report from Tribune, which owns 26 TV stations and 11 daily newspapers, including the Chicago Tribune.